insulating an unheated marble floor

butterscotch

Hi --

Former owners installed a marble floor in the kitchen, and removed the old hot-water rad in the room to make space for a pantry cupboard.

Looks nice, but in Toronto, the winters are cold! and the kitchen floor, and air temp., are freezing.

I'm considering getting kickspace heaters installed. If I do, electric is the way to go (even though power rates are sky-high here) because the cost of hooking hot water kickspace heaters into our old boiler system is in the many thousands, and I have surplus heavy duty outlets in the kitchen that could be converted to provide power for heaters.

Even so, it's not worth installing heaters without insulating the floor from underneath.

What is the easiest, most cost-effective material and method?

I've thought about stapling that shiny foil bubble-wrap stuff to the exposed floor joists.

Another option: fibreglass batts shoved up in between joists -- but would I need a moisture barrier? Would I need to cover up the batts with cheap tile or something, to ensure the insulation doesn't get dirty (it's an old, unfinished and unheated basement) or fall down?

Yet another option: spray foam insulation, but I've heard it's really, really pricey. Also might necessitate moving wiring -- you can't spray over power supply, right?

Last option: rigid foam panel insulation, cut to fit between joists -- which I think I've heard has low R value and is also expensive.

Also, should I do kitchen first, then do rest of underside of first floor (which is hardwood in other places) as time and money permit?

Will it make a big diff. to heat bills?

Thanks for input on costs, and ease of installation for various insulation methods.

CplDevilDog

Could you install radiant heating under the sub-floor (from the basement)? Is the sub-floor OSB/Plywood or plank?

Is there a concrete slab in the basement or just dirt? If there is, they may have poured it with the correct vapor barrier, in which case you would not want to double that.

If its just dirt, I would put down 6mil poly now just to reduce the amount of moisture rising (do your windows condensate on the inside in the winter?)

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creeper

I realize you are asking about insulating the cold floor, but you can't under estimate the value of making sure you have enough insulation in the attic. I had blown in installed in the attic and realized a huge and immediate diff in both the hydro bill (electric furnace at the time, but have since upgraded to gas) AND the comfort level of the house. Heat rises, so keep what you paid for in the house

butterscotch

Hi --

I've thought about installing electric radiant from underneath, but the underfloor is plank (probably with plywood on top of it, since I can't see the underside of the marble between planks, looking up from basement).

There's a very old concrete slab floor, cracked in places. We do get some condensate between windows in winter. I haven't noticed it in the basement, but upstairs there is a bit -- possibly b/c of window type (metal sliders).

air in house is pretty darn dry in winter.

Butterscotch

CplDevilDog

I would think the heat from an under floor system would transfer through the floor pretty well since you don't have any thermal breaks in the floor system.

It wouldn't be as efficient as if you had just the plywood but I don't think it would be a waste either. No personal experience with under floor systems though.

Just thoughts

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butterscotch

Thanks, but I've pretty well ruled that out b/c I'd have to insulate the floor under the radiant heat system anyway.

Electric kickspace plus insulation is most efficient and economical, so I just have to decide on insulation method.

From what I've heard, fibreglass looks like best option.

Canucker

Do you have any pics of the area where they took the rad out and the boiler near piping? In your other thread of the same topic, I wondered why you were told it would be many thousands to repipe a section of it.

Creeper, hot air rises, heat radiates to cold, regardless of direction.